Ludwig and Chow introduced the entity of stretched scar as a separate entity in the domain of secondary strabismus11,12. In the stretched scar-induced strabismus, secondary deviations occur months to years after the primary procedure, in contrast to the slipped muscle, in which the secondary strabismus occurs in the immediate postoperative period13. This case series shows clinical characteristics and results of management of secondary strabismus caused by stretched scar. Overall, stretched scar-induced secondary strabismus should be suspected in cases with late over or undercorrections associated with limited duction of the previously operated muscle. Management which includes exploration, excision of the scar tissue and reattachment of the muscle to the sclera using non-absorbable sutures is usually effective in restoration of normal muscle function. However, additional surgery of antagonist muscles might be needed in selected cases.
In this case series, the average interval elapsed between the primary procedure and correction of stretched scar induced strabismus was 7.7 months (range; 2-36), a significantly smaller interval when compared with 10, 13 and 29 years that were reported in previous trials11, 15, 18. The long-time interval reported in the previous trials could result from the relative non-familiarity of the issue of stretched scar as a cause of residual or consecutive strabismus.
The issue of the stretched scar was addressed in few previous reports. Most of those reports dealt with the stretched scar as a cause of consecutive exotropia following recession of both medial recti for the treatment of esotropia. In one case series, which addressed stretched scar-induce consecutive XT; mean XT was corrected from 33.1PD to 12PD after 4months of scar excision combined with single medial rectus muscle advancement using absorbable sutures18. In the consecutive XT subgroup of the current series (3 cases), mean angle of deviation was improved from 38.4 PD XT to 14.3PD ET after combined excision of the scar tissue and MR advancement. In 2013, Cho and Ryu evaluated their experience in management of consecutive exotropia by MR advancement following medial rectus recession for infantile esotropia. They have reported that slippage of the MR was the cause of consecutive deviation in 17 out of 77 patients19.
In the past, the underlying pathophysiology responsible for the development of late secondary strabismus associated with weak ocular duction was poorly understood. This had led Cooper20 to suggest treating cases of secondary strabismus by operating on the fresh muscles instead of the previously operated ones. However, the issue of stretched scar was not clearly understood until the observations of Ludwig and Chow which identified the stretched scar as the culprit for cases of late secondary strabismus associated with poor ocular duction, and also differentiated it from the previously well known “slipped muscle”. Several methods have been used to control excessive fibrosis and scarring which could restrict ocular motility and predispose to postoperative induced deviations, and they include the use of amniotic membrane21, application of mytomycine-c22 and injection of triamcinolone23. However, their use in regular practice was limited by their complex intraoperative applications, inconsistent results and development of complications24.
Despite its retrospective nature, small sample size and short follow-up, this trial agrees with the work of Ludwig and Chow in that the stretched scar should be suspected in any case of overcorrection (following previous recessions) and undercorrections (after previous resections) accompanied with any degree of poor muscle duction. Key factors in diagnosis of stretched scar are the late onset and the slowly progressive course of late deviations associated with variable degrees of weakness of ocular duction. Intraoperative forced duction test, which is usually negative in these cases, is used to differentiate stretched scar from tightness and stricture of the antagonist muscle especially if unilateral recess-resect was the primary procedure.